Neural crest cells arise during neurulation in early vertebrate embryos, migrate extensively, aggregate at specific sites, and ultimately give rise to a wide variety of different cell types in the adult, including most of the neurons and glial cells of the peripheral nervous system, endocrine cells, pigment cells, and much of the connective tissue of the face and neck. To generate this cellular diversity, it is believed that during and following migration, different crest cell populations undergo different sets of developmental restrictions. In this way, the various crest-derived populations become progressively restricted to either one or another of these lineages. We wish to understand the molecular nature of these developmental events, and how they are regulated during development. To this end, we have generated a cDNA library from mRNA transcripts isolated from a population of crest-derived cells in the posterior branchial arches (BAs) of avian embryos. Presumably, some of the transcripts specific to posterior BA cells mediate developmental events known to be occurring in these cells, including developmental restrictions, neurogenesis, and cellular aggregation. We now propose to use this cDNA library to identify such gene transcripts. To begin, we will determine which neural crest-derived and non-crest-derived tissues express these transcripts and at what developmental stages. This will allow us to correlate the appearance of specific mRNA transcripts with known developmental events. From sequence analysis of mRNAs which show "interesting" developmental appearances, peptides will be synthesized against their predicted amino acid sequences in order to generate antisera for immunocyto-chemical localization studies of their gene products. We also plan to identify genes which are coordinately expressed by the crest-derived cells of the posterior BAs in order to test the hypothesis that these genes share sequence homologies in their vicinity. These shared sequences may mediate the coordinated expression of genes, for example, by binding common DNA-binding proteins. Finally, we hope to identify genes coding for proteins known to be specifically expressed in the posterior BAs, including a novel intermediate filament-associated protein--"NAPA-73". This protein is one of the earliest markers of neurogenesis in both the peripheral and central nervous systems.